1. Field of the Invention
The present invention relates to a resin composition for injection molding that has good moldability, such as spiral flow, and also has excellent transparency, excellent impact strength and tensile strength at normal and low temperatures, and good heat resistance while possessing good balance between strength and rigidity, and that may be advantageously used to form injection-molded products.
2. Description of the Related Art
Materials which have been used to produce food containers of flexible resins, such as Tupperware (registered trademark), include high-density polyethylene, polypropylene, high-pressure low-density polyethylene, and linear low-density polyethylene.
High-density polyethylene is disadvantageous in that it has poor flexibility and poor transparency. As a result of the poor transparency of high-density polyethylene, when a container made of this material contains objects therein, the contents cannot be seen or cannot be readily seen through the container. Thus, the practical value of such containers is reduced, and the range of use to which the containers can be applied is limited.
Polypropylene has relatively good transparency, and has good dynamic properties at normal temperature. However, polypropylene has insufficient strength at low temperatures. As a result, when polypropylene is used in freeze-preservation, cracking or whitening tends to be caused by the application of local stress. In addition, polypropylene has poor flexibility, with the result that, when a container made of polypropylene is bent to a relatively great extent, an irreversible whitening line may be formed, or the original shape cannot be readily recovered.
High-pressure low-density polyethylene is another material that has relatively good transparency. However, this material does not have sufficient heat resistance to be applicable in such uses as microwave ovens. In addition, high-pressure low-density polyethylene does not have enough resistance to environmental (stress) cracking (referred to as "ESCR") to be applicable in fields where resistance to acids and bases, resistance to oils, and/or resistance to chemicals are required. Thus, high-pressure low-density polyethylene only has limited range of application.
Linear low-density polyethylene has been introduced as a resin capable of overcoming the problems of the above resins. However, linear low-density polyethylene has not yet acquired the level of transparency required by the market, nor does it have sufficient flexibility.